A zeolite is a crystalline hydrated aluminosilicate that may also contain other metals in the crystalline framework of the zeolite crystal or deposited on its surface. The term “zeolite” includes not only aluminosilicates but substances in which the aluminum is replaced by other trivalent elements. Silicon may also be replaced by other tetravalent elements. Generally, zeolites are tetrahedra structures of the formula TO4, which form a three dimensional network by sharing oxygen atoms and wherein T represents tetravalent elements, such as silicon, and trivalent elements, such as aluminum.
Zeolites are typically prepared by preparing an aqueous mixture of silicon oxide, aluminum oxide and, optionally, oxides of other trivalent or tetravalent elements; and maintaining the aqueous mixture under crystallization conditions until crystals of zeolite form. In the crystalline structure there are pores and channels which may be interconnected. The dimensions and configuration of these pores and channels allow access of molecules certain size or configuration, thus promoting the selectivity to certain products. Elements, such as metals, may be also deposited on the zeolite to facilitate selectivity or catalytic enhancement of the zeolite catalyst.
One particular use for zeolite catalysts is in the aromatization of alkanes and/or olefins. While useful zeolite catalysts for this process exist, improvements in zeolite catalysts that provide high selectivity for aromatics, or other products, and that provide high conversion with long catalyst life are still desired.